The present invention pertains to a process and device for manufacturing networks of microlenses and, especially, to a process in which a plate of malleable material is pressed against a grooved nonmalleable surface of a consistent network of pits in which at least the openings correspond to the contours of the convex parts of the microlenses, which are formed by permanent pressing of the plate against the pitted surface. The present invention also pertains to a device for implementing this process.
At the present time, networks of optical microlenses are used in various applications and, especially, for taking and reproducing images. In this technical field, we know of video image projectors that function by projecting light across a two-dimensional matrix of liquid crystal cells showing the image to be projected. These image projectors have a low luminous yield due to various levels of light absorption by polarizers placed on both sides of the matrix, by opaque margins of the cells of the matrix, by the projection screen, etc. For this reason, it is possible to improve the present luminous yield (on the order of 1%) by a factor of 2 or 3 by focusing the light source on the useful areas of the liquid crystal cells, which are selectively interchanged between an opaque state and a transparent state. Thus, we avoid absorption by the opaque margins of these cells. This absorption problem is also found in other devices, such as backlighted liquid crystal screens that are used in data processing for displaying information.
When one takes into account the dimensions of the matrices of liquid crystal cells in present use and the high definition now contemplated for video images intended for the general public, one must then arrange two-dimensional networks of microlenses distributed on the order of 100 xcexcm. An example would be a network of lenses between several hundred thousand and several million.
From French Patent No. 9,408,420, filed on Jul. 7, 1994 by the applicant, we know that we can create such networks with a process of the type mentioned in the preamble of the present description. According to this process, a plate made of a malleable optical material is pressed against a nonmalleable pitted surface by subjecting the two sides of the plate to different pressures. The pressure on the side facing the pitted surface is less than the pressure established on the other side of this plate. The depth of the pits is greater than the thickness of the convex part of the microlenses formed by permanently bending the plate against the pitted surface. The absence of contact between the bottom of the pits and the convex parts of the microlenses preserves an xe2x80x9copticalxe2x80x9d finish for these parts.
In order to implement this process, the previously cited French patent application proposed a device containing a waterproof housing for fluid, a support means of optical material for the plate, and a rigid sheet with a pitted surface. They are parallel and close to each other. The plate thus constitutes an element of the housing""s wall. This patent application also proposed a means for establishing different fluid pressure levels in the housing compared to that on the side of the plate opposite the plate limiting the housing, so that this plate is pressed against the pitted surface upon activation of the means used to establish pressure. In order to increase the productivity of this device, it can include a multiplicity of superposed housings. Each housing is limited by two optical plates on opposite sides and each is placed next to a corresponding pitted surface. The means for establishing fluid pressure in these housings operate in parallel.
By producing several networks of microlenses at the same time, we obtain the desired increase in productivity. Nevertheless, the device must also include a multiplicity of superposed housings having the appearance of a complex stacking of plates made of optical material, sheets with a pitted surface, supports, crossbars, and sealing gaskets. The assembling and disassembling of such a complex device limits the productivity of the described device.
The purpose of the present invention is to allow a process and a device for manufacturing networks of microlenses designed in order to ensure a high productivity, being suitable for industrial production in a large volume and at a low manufacturing cost.
Along with other aspects that will become known during the reading of the following description, the goal of the invention is reached by a process for manufacturing networks of microlenses of the type described in the preamble of the present description. It is remarkable in that one forms a group composed of a multiplicity of plates of malleable material and a multiplicity of generally flat molds in which each contains at least one nonmalleable pitted surface. These last objects are inserted between the plates so that at least one side of each of the plates is arranged opposite a pitted surface of a mold. A noticeably uniform pressure oriented perpendicularly to the surface of the plates is applied to the entire group, as it has been produced.
The group of plates and molds is quickly assembled and disassembled. It can even be done automatically. The setting of successive pressure for such groups of plates can also be automated, which allows reaching the desired high level of productivity.
Following another characteristic of the process according to the invention, one ensures isostatic pressing of the group of plates and molds, so as to produce networks of microlenses having uniform optical characteristics on the entire surface of the network.